The 50 patients who are treated in the double-blind controlled study of ursodeoxycholic and chenodeoxycholic acids will be treated for at least two years in a double-blinded fashion. Treatment will be discontinued in those patients who completely dissolve their stones. These patients will be followed in order to study the recurrence of gallstones after dissolution. Ultrasonography of the gallbladder will be obtained every other year. If there is recurrence of stones, the patients will again be treated with the agent which has previously been successful. The patients in whom there is no dissolution of gallstones will be placed on either ursodeoxycholic or chenodeoxycholic acid if they had been treated with placebo before. If the patient has been treated with chenodeoxycholic acid previously, then he will be placed on ursodeoxycholic acid and vice versa. Biliary lipids and bile acid kinetics will be determined after completion of treatment. During treatment the patient will be examined on a two-monthly basis and laboratory tests will be performed which include liver function tests and serum lipoprotein analysis.